In an embedded control system, the interaction between the digital units, such as a controller, and the analog units, such as a controlled plant, of the system is critical. This interaction is accomplished generally by signal conditioning hardware, such as analog-to-digital (AD) and digital-to-analog (DA) converters. The signal conditioning hardware transforms low-power electrical signals in the operational range of logic signals (e.g., 0-5V) to high power signals to drive transducers, such as pumps, motors and valves, or vice versa.
‘Smart sensors’ (such as the IEEE 1451 standard) alleviate the burden of signal communication between the digital and analog units of a system. The smart sensor includes a microprocessor that contains information about the measurement of the sensor, such as the unit and accuracy of the measurement. The microprocessor then communicates directly in terms of signal values instead of having to convert them in binary representations that concur with the selected digitization and gain of the signal conditioning hardware.
In some text-based programming environments, users are allowed to use high-level signal definitions or descriptions instead of having to provide a sequence of hardware dependent commands to obtain a certain set of data. The high-level signal definitions or descriptions define or describe signals regardless of the hardware that generates or measures the signals. There are many standard signal definition or description languages available for traditional text-based programming languages that allow users to define or describe signals, apply signals, and measure signals. In those languages, users do not need to care about the hardware used to generate or measure the signals. For example, the Abbreviated Test Language for All Systems (ATLAS) allows standard signal operations, such as APPLY, MEASURE and VERIFY. Another example of the signal definition or description standard can be found in the “IEEE P1641” standard.
Recently, graphical programming environments are widely employed to model and simulate engineering and scientific systems, including embedded control systems. The graphical modeling environments provide tools for creating graphical models of the systems and for executing the graphical models. Exemplary graphical modeling environments can be found in time-based block diagram modeling environments, such as those found within Simulinkφ from The MathWorks, Inc. of Natick, Mass., state-based and flow diagram modeling environments, such as those found within Stateflow® from The MathWorks, Inc. of Natick, Mass., data-flow diagram modeling environments and Unified Modeling Language (UML) modeling environments. In these graphical modeling environments, the high-level definitions or descriptions of signals are also needed for the users to create and simulate the graphical models regardless of the hardware that generate or measure the signals.